1. Field of the Invention
The present invention is related to a zoom lens and an image pickup apparatus having the same. The zoom lens may be preferably used in an image pickup apparatus having an image pickup element, such as a digital still camera, video camera, monitoring camera, broadcasting camera, or the like, or a camera using silver-halide photography film, or the like.
2. Description of the Related Art
As of recent, image pickup apparatuses such as digital still cameras, video cameras, and so forth, which use solid state image pickup sensor-elements are highly functional and have reduced in overall size. Accordingly, there is demand for a zoom lens for use with these apparatuses. To meet the demands of these highly functional and small sized apparatus, a zoom lens should preferably have high power, a wide view angle, small size, and good optical performance over the entire zoom range. To this end, certain zoom lenses have already been proposed. Currently, there are known zoom lenses having lens units with positive, negative, and positive refractive power, as seen from the object side toward the image side, in that order.
However, as the functionality of image pickup apparatuses continues to improve, zoom lenses must follow such improvement. To that end, it is known that raising the power of a zoom lens increases the focal length at the telephoto end. However, occurrence of axial chromatic aberration becomes overly pronounced. Zoom lenses disclosed in Japanese Patent Laid-Open No. 2008-191291 and Japanese Patent Laid-Open No. 2008-191286 use anomalous dispersion glass for the material of a negative lens included in a first lens unit, as a technique to reduce axial chromatic aberration.
Generally, a small-sized and high-powered image pickup optical system can be obtained by increasing the refractive power of each lens making up the image pickup optical system while reducing the number of lenses making up each lens unit. However, increased refractive power of a lens unit increases the refractive power at the lens surface of the lenses making up the lens unit, resulting in a thicker lens to ensure a sufficient edge thickness for the lens. This results in a larger front lens diameter (effective diameter of the front lens), which makes realizing reduction in size of the optical system difficult. Also, increased focal length at the telephoto end results in pronounced chromatic aberration, which is difficult to correct.